Method of forming uranium monocarbide



Patented Sept. 25, 1951 METHOD OF FORMING URANIUM MONOCARBIDE James H.Carter, Blacksburg, Va., and Adrian H. Daane, Ames, Iowa, assignors tothe United States of America as represented by the United States AtomicEnergy Commission N Drawing. Application March 26, 1947, Serial No.737,430

metal and carbon.

It is an object of this invention to provide an efiicient process forthe preparation of uranium monocarbide.

Other objects and advantages of this invention will be readily apparentfrom the following del0 scription of preferred embodiments of ourinvention.

Broadly stated, it is well-known in the art that uranium and carbon maybe heated in comminuted contact with each other at an elevatedtemperature for a sufficient time to form uramum-carbon compounds oralloys. These temperatures are in excess of the melting point ofuranium; and the compound thus produced contains a composite mass ofuranium dicarbide (U02) and uranium sesquicarbide (U 03).

In accordance with an embodiment of the present invention the existenceof another specific uranium carbide, uranium monocarbide,

is established by metallographic examination of a mass produced bycontactin uranium and carbon in stoichiometric proportions at atemperature less than the melting point of the uranium metal.

The solubility of carbon in solid uranium is less than in the liquidphase which occurs at a temperature in excess of 1125 C. The solubilityof carbon in solid uranium has been experimentally determined. Thesolubility of carbon in the gamma phase, wherein the temperature of thesolid metal is in excess of 770 C. is of the order of 0.05 percent (1atom percent carbon). The uranium metal containing 0.05% carbon shows asubstantial dissolution of the carbide when,

annealed approximately 96 hours at 1000 C. The 4 upper limit of thesolubility of carbon in the betauranium within a temperature range of660 C. to 770 C. is of the order of 0.03 percent (0.6 atom percentcarbon) while in the alpha phase wherein the uranium metal is at atemperature less;

than 660 C. the solubility is not much greater than 0.01 percent (0.2atom percent carbon).

In examining the metallographic crystal structure of the carbideformation in the uranium mass wherein the reaction temperature was keptbelow 1125 C. (melting point of uranium), a dendritic structure existedin the form of cubic faced-centered crystals (probably NaCl-structure),isomorphous with those of UN and U0.

According to observations, the carbon in uranium monocarbide can bereplaced by Oxygen or nitrogen to give a slight decrease in the latticeconstant (as low as 4.936 5. when U02 is found) and therefore the mostreliable value of the lattice constant is the highest one obtained,primarily 4.951 A. The lattice constant of uranium monocarbide does notmarkedly depend upon the presence of an excess amount of uranium orcarbon, thus indicating low solubility of both components in thecarbide.

In examining the uranium carbon system, it shall be noted that evidencefor the existence of a high temperature compound is somewhat slight,although Widmanstatten patterns of alloys between uranium sesquicarbide(U2C3) and uranium dicarbide (UCz) have been interpreted as indicatingthe existence of solid solutions of aUzCs and .pUCz. No carbides withmore than two carbon atoms per uranium atom seem to exist although thereis some X-ray evidence, however, for solubility of carbon'in the UCzlattice; particularly at temperature near the melting point (2375 C.) ofthe uranium dicarbide alloy.

The system diagram shows that where the stoichiometric proportions ofcarbon to uranium exceed 4.8% by weight of carbon there is a greatertendency to form the UCz structure and probably the U203 structure,depending on the temperature. When the stoichiometric percentage ofcarbon is reduced to less than 4.8% of carbon, the tendency of thereactive mass of uranium and carbon to form uranium monocarbide isenhanced; that is, at a temperature less than the melting point of theuranium metal (1125 C.).

A mode of preparing uranium monocarbide consists in mixing powdereduranium metal with powdered carbon in stoichiometric proportions whereinthe carbon content is less than 4.8% of the composite mass content, thenpressing the mixture into small blocks under high pressure, 20-50 tonsp. s. i., for example, and then heating the pressed blocks in atemperature range less than the melting point of uranium, preferably atabout 900-10009C. for about hours.

Another method of forming uranium monocarbide is to compositely mixcomminuted uranium and carbon in stoichiometric proportions to formuranium monocarbide, and then pressing the mixture into small blocksunder high pressures, about 50-100 tons p. s. i., for example, thenheating the pressed blocks in a temperature range above the meltingpoint of the uranium metal and less than the melting point of theuranium carbide produced, 2250 0., whereby a mixture of UCz and U203 isformed, and then quenching the composite mass to a temperature less thanthe melting point of the uranium metal at about 900 C. The carbon alloythus formed will disproportionate into uranium dicarbide containinguranium monocarbide and carbon, independently 'of an excess "componentin the melt.

In the foregoing process of producing uranium monocarbide, anotherembodiment consists "of heating uranium metal of high 'purity'contentwith carbon in a stoichiometric amount of: about 4.8 per cent atsubatmospherio pressure at a temperature in excess of 1125 .C. and 'thenquenching the uranium-monocarbide composition to a temperature of about900 C.

In another embodiment of the present invention, it was found thaturaniummono'c'ar'bide may be produced by heating uranium metal of highpurity content with carbon in a stoichiometric amount of about 4.8 percent by weight .in acar-bon dioxide atmosphere at a temperature between900 C. and 1125 C.

:Numerous variations and modificationsin the preferred methods andexamples described will be readily apparent andmay be made withoutdeparting from the spirit and scope of our inven- .tion as defined inthe following claims.

This application is a continuation-in-part of .our co-pendingapplication, Serial No. 549,282, filed August 12, 1944, now Patent No.2,526,805.

The method of forming uranium monocarbide by heating uranium oxideandcarbon and the .product are the subject matter of Patent 'No.2,448,479, .granted to Harley A. Wilhelm and .Adrian H. Daane on August31, 1948.

What is claimed is:

1. The process of producing uranium monocarbide which comprises heatinguranium metal in contact with carbon in approximately stoichi- .ometricamount at a temperature sufliciently high to react but below the meltingpoint 'of uranium.

2. The processof producing uranium .imonocarbide-which comprises heatinguraniummetal of high purity with carbon in a "stoichiometric ;amount ofabout 4.8% by weight in a carbon dioxide atmosphere at a'temperatureatbetween approximately 900C. and 1125 C.

3. A process of producing uranium monocarbide which comprises heatinguranium in contact with carbon at a temperature in excess of themeltingpoint of uranium so 'as toform a uranium-carbon mass consistingessentially of uranium, U02 and U203 and then quenching and maintainingsaid mass at a temperature below the melting point of uranium butsufliciently high to form uranium monocarbide.

4. The process of producing uranium monocarbide which comprises heatinguranium metal of high purity in contact with carbon at'a temperature inexcess of the melting point of the .uranium metalso' as to form auranium carbon alloy consisting essentially of uranium, Ucz'and UzCs,and then quenching and maintaining said alloy at a temperatureaboveabout'900 C.

amount of about 4.8% at a temperature in excess of the. melting point ofuranium metal whereby --a mixture of uranium, UCz and U2C3 is obtainedand then quenching and maintaining at a temperature "of about 900 C.

"I. The process of producing uranium monocarbide which comprises heatinguranium metal of high purity with carbon in a stoichiometric amount ofabout 4.8% at sub-atmospheric -pressure at a temperature in excess of1125 C. whereby a mixture of uranium, UCz and UzCa is obtained and thenquenching and maintaining at a temperature of about 900 C.

8. A process for producing uranium monocarbide, comprising reacting auraniumand carbon-containing mixture selected from the group consistingof a mixture of uranium plus carbon in about stoichiometric amounts anda mixture of uranium and U02 plus U203 in which the total uranium andthe total carbon contents are present in approximately stoichiometricproportions by heating the mixture to a temperature sufficient tobring-about reaction but below the melting point of metallic uranium andmaintaining said temperature for reaction and formation of uraniummonocarbide.

9. A process for producing uranium monocarbide, comprising reacting auraniumand carbon-containing mixture selected from the group consistingof a mixture of uranium plus carbon in which uranium is present in atleast stoichiometric amounts and a mixture of uranium, UCz and U2C3 inwhich the total uranium is present in at-least stoichiometricproportions astonranium monocarbide by heating them-ixture to atemperature sufficient to bring about reaction but below the meltingpoint of metallic uranium, and maintaining saidtempe-rature for reactionand formation of uranium monocarbide.

10. A process for producing uranium mono- .carbide, comprising reactinga mixture of uranium, UCz and U203 in which the total uranium ispresentin at least stoichiometric proportions as to uraniummonocarbideby heating the mixture toa temperature suiiicient to bring'aboutreaction but below themelting point of metallic uranium and maintainingsaid temperature for reaction and'formation of uranium monocarbide.

JAMES H. CARTER. ADRIAN H. DAANE.

No references cited.

9. A PROCESS FOR PRODUCING URANIUM MONOCARBIDE, COMPRISING REACTING AURANIUM- AND CARBON-CONTAINING MIXTURE SELECTED FROM THE GROUPCONSISTING OF A MIXTURE OF URANIUM PLUS CARBON IN WHICH URANIUM ISPRESENT IN AT LEAST STOICHIOMETRIC AMOUNTS AND A MIXTURE OF URANIUM, UC2AND U2C3 IN WHICH THE TOTAL URANIUM IS PRESENT IN AT LEASTSTOICHIOMETRIC PROPORTIONS AS TO URANIUM MONOCARBIDE BY HEATING THEMIXTURE TO A TEMPERATURE SUFFICIENT TO BRING ABOUT REACTION BUT BELOWTHE MELTING POINT OF METALLIC URANIUM, AND MAINTAINING SAID TEMPERATUREFOR REACTION AND FORMATION OF URANIUM MONOCARBIDE.